1. Field of the Invention
This invention relates to the hydroisomerization of wax and/or waxy feeds such as waxy distillates or waxy raffinate using a combination of catalysts to produce lube basestocks of increased viscosity index and/or improved volatility.
2. Description of the Related Art
The isomerization of wax and waxy feeds to liquid products boiling in the lube oil boiling range and catalysts useful in such practice are well known in the literature. Preferred catalysts in general comprise noble Group VIII metal on halogenated refractory metal oxide support, e.g. platinum on fluorided alumina. Other useful catalysts can include noble Group VIII metals on refractory metal crude support such as silica/alumina which has their acidity controlled by use of dopants such as yttria. Isomerization processes utilizing various catalysts are disclosed and claimed in numerous patents, see U.S. Pat. No. 5,059,299; U.S. Pat. No. 5,158,671; U.S. Pat. No. 4,906,601; U.S. Pat. No. 4,959,337; U.S. Pat. No. 4,929,795; U.S. Pat. No. 4,900,707; U.S. Pat. No. 4,937,399; U.S. Pat. No. 4,919,786; U.S. Pat. No. 5,182,248; U.S. Pat. No. 4,943,672; U.S. Pat. No. 5,200,382; U.S. Pat. No. 4,992,159. The search for new and different catalysts or catalyst systems which exhibit improved activity, selectivity or longevity, however, is a continuous ongoing exercise.